A/DA Definition Preamp / Boost

This is way more than a simple boost pedal

Boost pedals are one of the oldest pedal effects categories and often (but not always, as we'll soon see) some of the simplest pedal circuits. Many only utilize a single transistor in their designs. Some, like the classic Dallas Rangemaster treble boost, use older germanium transistor-based circuits and are intended to "color" the sound of the signal going through them; adding emphasis to the upper mids and even some slight grit of their own. However, not all "boosts" take this same approach. Today we'll be looking at one that has cleanliness and transparency as its design goals.

California's A/DA is no stranger to designing preamps for guitarists. Their MP-1 MIDI programmable rack mount tube preamp was incredibly popular in the 1980s, and is still used and cherished by many guitarists even today. Let's see if they've put that knowledge and experience to work in their new solid state preamp / boost pedal. Dubbed the Definition, does the pedal do the name justice?

What You Need To Know

• The ADA Definition is a solid state preamp in pedal format, with a handy onboard boost function. It is designed to help you get the most out of magnetic pickups, and it will work equally well for both guitar and bass.

• The ADA Definition is built into a rugged all-steel enclosure measuring 4.5" L x 2.5" W x 1.5" H. The rugged build is more than skin deep, with thick glass epoxy circuit boards and high quality components such as hand-selected low-noise FETs located inside. Construction uses three circuit boards; one for the footswitch, one for the I/O and power jacks, and a third one for the main circuitry. They connect via molex connectors. The quality of the build is readily apparent.

• There are two external switches on the Definition - a standard footswitch, and a slider switch. The slider switch, which is labeled "Bypass / In" serves as a true bypass switch for the entire preamp. I noticed a slight bit of pop when engaging the slider switch, but it's not a big deal since most players will turn it on and leave it on. When it is in the Bypass position, the preamp is off, and the footswitch will not have any effect on the sound. When it is set to the In position, the preamp is activated, providing all of the impedance benefits that the Definition has to offer.

• The footswitch becomes active when the slider switch is in the In position, and when activated, it kicks in the Definition's boost function. A blue LED illuminates when the boost is activated, and switching in the boost is completely silent. The amount of boost is set by the single large Boost knob on the top of the pedal. Up to 16dB of boost is available, which makes the Definition great for boosting your volume level for solos. It also works very well for kicking a tube amp that's set on the edge of distortion over the top and into full overdrive, and it can be used to do similar nasty things to your favorite distortion, fuzz and overdrive pedals, helping them generate new and even heavier tones than they'd be able to provide on their own.

• Access to the interior of the pedal is going to be challenging for some, since ADA uses six pointed screws for construction - you get the feeling they really don't want you poking around in there, and to be fair, there's really no reason to open the pedal up since there are no user adjustable trim pots or switches mounted inside; so to keep your warranty intact and to satisfy your curiosity, I'm including some "gut shot" pictures.

• Speaking of the warranty, the A/DA Definition comes with a one year non-transferable parts and labor warranty. It was designed and is built in California, and each unit is fully tested and burned in at the factory before being shipped to insure quality and reliability.

• While I did not disassemble the pedal completely, I was able to see enough of the interior to say that this is far from a simple single transistor boost design. There are at least six transistors used in the Definition, including two 2N5088 -B49 and one 2N5087 E35 - the others I was unable to see well enough to identify without removing the circuit boards.

• Four clear rubber feet are provided, but not pre-installed, which allows you to attach them if you want, or leave them off and add your own Velcro instead for pedalboard mounting.

• Powering options are somewhat limited. There is no battery compartment, so you'll have to stick to external power. The A/DA Definition can accept anything from 9 to 18 volts DC, and has a industry-standard 2.1mm center negative power receptacle located at the top of the pedal near the 1/4" input and output jacks. A/DA recommends using at least 12 volts when using the Definition with bass for increased headroom. They thoughtfully include a regulated wall wart style power supply with the pedal that provides 100mA at 9 volts, or 5mA at 18 volts. A/DA does not recommend using unregulated power supplies, but you'll be fine with most high-quality brick-style pedalboard power supplies should you opt to use one.

• The A/DA Definition is a very nice boost, but its greatest contribution to your sound lies in its low noise, wide bandwidth (A/DA lists the frequency response as flat from 20 Hz to 40 kHz, +/- 0.1dB) and impedance optimization capabilities. With a very high input impedance of 3 megohms, it's not going to load down your pickups. This means better dynamics and wider-range frequency response - more of the signal passes through unimpeded, resulting in a more high-fidelity sound and wider bandwidth. The output impedance is also unusually low at a mere 100 ohm.

• If you're running a lot of pedals, or long lengths of cable and don't have a buffer in your signal path, the A/DA Definition Preamp will definitely benefit you, removing the dull and dark veil that is currently coloring your tone.

• With its low noise and high bandwidth, the A/DA Definition Preamp is also a great tool for direct recording and reamping.

Limitations

• Bike chain link pedalboard mounting would require a bit of adaptation and modification, and this would most likely void your warranty.

• The ADA Definition is best suited for use with magnetic pickups. Users of active pickups will not benefit much from its impedance optimization capabilities since most active pickups already have low impedance output.

• When used in front of some vintage style fuzz pedals, the A/DA Definition may change the interaction between the guitar and fuzz. For example, when used with my Monsterpiece MkII (a Mk 1.5 based Tonebender type fuzz) the guitar's volume knob needed to be turned down considerably more before it "cleaned up." You may prefer to place the Definition later in the signal path in order to insure the usual interaction between the fuzz and guitar. Alternatively, since it's true bypass, you can place it in front of the pedal and turn it off when using the fuzz. I preferred it after fuzz so that I could still utilize the boost function while benefiting from the A/DA's low impedance output.  

• Even when the pedal is bypassed via the slider switch, depressing the boost footswitch still illuminates the LED indicator, which may lead to some confusion as to whether the pedal is "on" or not. There is no separate power or "active" LED indicator for showing when the preamp is active but the boost is off.

Conclusion

The Definition is far more than a simple boost pedal - it's a very low-noise and transparent preamp with a boost function built-in. Clean tones are wonderful, and the boost function is very useful for helping you generate dirty tones in partnership with your dirt pedals and tube amps too. The Definition optimizes your input and output impedance and helps you get the best from your magnetic pickups, increasing the frequency bandwidth and bringing increased articulation dynamics and yes, definition to your sound. It's not going to provide as much benefit for those who use active pickups, but even then, its boost feature could still come in handy. Whether or not the boost function alone will justify the price for users of active pickups is debatable, but for the majority of players who rely on passive magnetic pickups, and especially for those who record direct, or run large pedalboards and extended length cables, the A/DA Definition preamp can make a significant difference to the overall sound quality of their rigs.

Resources

A/DA Definition Preamplifier for Guitar and Bass with Boost ($199.95 "street")

A/DA product web page

Phil O'Keefe is a multi-instrumentalist, recording engineer / producer and the Senior Editor of Harmony Central. He has engineered, produced and performed on countless recording sessions in a diverse range of styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow Skulls, John McGill, Michael Knott and Alexa's Wish. He is a former featured monthly columnist for EQ magazine, and his articles and product reviews have also appeared in Keyboard, Electronic Musician and Guitar Player magazines.